64 M. Balbiani on the Reproduction 
this point of the cells composing it; and the internal granular mass 
projects through this orifice. We then clearly perceive, either 
directly or by means of reagents, that the whole inner surface of 
the blastoderm is lined with a delicate membrane which extends 
like an envelope round the central vitelline mass. 
It is this membrane, with a portion of its contents, that pro- 
jects, as just stated, through the orifice at the posterior extre- 
mity of the blastoderm. This hernial portion attaches itself to 
the corresponding epithelial cells of the ovarian chamber, which 
are hypertrophied, and becomes as it were engrafted upon them. 
When this connexion is established, the vitelline vesicle becomes 
constricted in the interior of the cavity of the blastoderm like a 
cell in process of division, and then separates into two juxta- 
posed secondary cells,—the posterior adherent to the epithelium 
of the chamber, the other, or anterior, being completely free in 
the above-mentioned cavity. I have sometimes succeeded in 
detecting a very pale granular nucleus in the posterior vesicle, 
and less distinctly in the anterior one; they, therefore, present 
all the characters of true cells. These vesicles or cells are to be 
the origin of the male and female generative elements of the 
future animal—that is to say, of the ova on the one hand, and 
‘the spermatic cells on the other. In fact, by a phenomenon of 
germination which I cannot describe here in detail, each of them 
becomes covered at its surface by a generation of small cells, 
which, when once produced, increase in size and continue to 
multiply on their own account. From this results the forma- 
tion of two very distinct cellular groups placed side by side in 
the cavity of the blastoderm. The group produced by the 
herniated vesicle engrafted upon the exterior epithelium repre- 
sents the male element, and will give origin to the fecundating 
corpuscles ; that which originates from the free vesicle in the 
interior of the ovum is, on the contrary, formed by the totality 
of the female elements—that is to say, the generative cells of the 
future ovules, surrounded by their nutritive cells. This latter 
group soon subdivides into a certain number of secondary groups, 
corresponding with that of the ovarian sheaths which are sub- 
sequently to be formed. The cells which compose it remain 
always transparent and colourless, and are also smaller than 
those of the first group, the cells of which, on the other hand, 
are soon permeated by numerous small green or yellow granula- 
tions, which enable them to be recognized with the greatest 
facility*. The generative vesicles of the two sexual masses be- 
extremity which is directed towards the external sexual orifice, and that of 
anterior pole to that which looks towards the terminal chamber of the 
ovarian sheath. 
* This yellow or green mass, which is met with in most Aphides at all 
